Unsteady flows in a centrifugal turbomachine is analysed in two-dimensional. Assuming incompressible and inviscid flow, the velocity field from the body surface is represented by means of source and vortex distributions. The blades of an impeller are represented by a lumped vortex and the case is by source panels. The wake of each blade is represented by a discrete vortex. A time marching method is used. To remove the high unsteady fluctuations at initial state, the impeller is forced to start slowly. This thesis is divided into three parts; an analysis of flow of an impeller alone, an analysis of flow of a turbomachine including the case and a study on the viscous separation occuring at off-design conditions. The head of the turbomachine is calculated by the unsteady Bernoulli equation. The head loss is calculated by empirical laws.
The result shows that periodic fluctuations of the head is caused by the interaction of the blade and the tongue in the case. The periodic fluctuations is one of the dominant noise source of the centrifugal turbomachine. The heads are compared with the experimental data, which show good agreements. When the separation is introduced, the flow fields are similar to the those shown in visualization experiment. The head is higher than that of no separation case and its value is agree with that obtain using the empirical law.
